The mobile data industry is evolving rapidly, resulting in exponential growth in demand for bandwidth. Service providers have foreseen an increasing data growth over the next few years. The growth in mobile data usage is being fueled by growing 3G penetration, popularity of smartphones and USB dongles, advanced mobile applications and flat-rate data plans. As a result, service providers are facing congested networks which are impacting their service delivery levels.
Many service providers are beginning to adopt a range of strategies, such as optimization of 3G networks using intelligent policy control, mobile data traffic offload, and transformation to 4G to reduce costs and alleviate congestion.
Mobile data offload, in particular 3G-WiFi offload, is becoming more and more popular these days. Offload is the ability to move mobile data traffic from one network to another in a way that is transparent to the subscriber, which is a key component of an effective network congestion reduction strategy. Mobile data offload will reduce costs and improve economies of scale by balancing traffic requirements across networks. The cost savings are significant. Service providers deploying a multi-access offload strategy can expect savings in the range of 20 to 25 percent per annum.
For example, AT&T has been in the forefront of using 3G-WiFi offload. AT&T hotspots automatically detect their subscribers and move their data traffic to WiFi. The whole process is completely transparent to the subscribers and the subscribers do not notice any difference.
Mobile data offload from 3G to WiFi presents a number of challenges to service providers. First, service providers must ensure that subscribers receive a consistent and comparable user experience regardless of access network, wherein service portability and continuity across multiple access networks is essential. Second, transparent sign-on is preferred, in which a single sign-on process is required to ensure seamless usage of various networks. Third, authentication access in non-3GPP networks, such as WiFi may not be easy when subscriber authentication data resides in the Home Location Register (HLR) in 3GPP networks. Fourth, smartphone users do not always have WiFi turned on due to the heavy battery drain on their handsets and network systems cannot force a device to switch on WiFi, which present challenges for service providers who want to offload traffic to WiFi. Fifth, the handset's connection manager requires knowledge of WiFi hotspot locations, in particular those in the vicinity of high-traffic cell sites that typically experience congestion. An offload solution also needs to be subscriber-aware, including subscriber location as it relates to available hotspots. Sixth, Simultaneous operation of WiFi and 3G is required, but not all handset manufacturers allow both 3G and WiFi to operate at the same time. In some cases, this can work but under a restricted condition where the WiFi acts as an Access Point (AP). Seventh, WiFi range is short, mainly due to the power of the WiFi transceiver on the handset. In most cases the link would be highly asymmetric, wherein the transmission from the access point would be able to reach the handset but the transmission from the handset is unable to reach the AP. This restricts the offload to happen when the user is static or very near to an AP. Eighth, there might be limited access to WiFi network. In most cases, there will be many WiFi networks in the vicinity of the user but it would be difficult to capitalize on these WiFi APs to provide 3G offload due to the lack of permission and necessary software to enable the switching.
FIG. 1 illustrates the standard protocol exchange between a mobile client and an AP in order for the mobile client to join a WiFi network.
As shown in FIG. 1, when the mobile client 101 tries to associate with the AP 103, it sends a probe request 111 to the AP 103. The AP 103, upon receiving the probe request 111, sends back a probe response 113 to the mobile client 101. The mobile client 101 then sends an authentication request 115 to the AP 103. The AP 103, upon receiving the authentication request 115, sends back an authentication response 117 to the mobile client 101. After authentication process, the mobile client 101 sends an association request 119 to the AP 103. The AP 103, upon receiving the association request 119, sends back an association response 121 to the mobile client 101. Accordingly, the mobile client 101 is associated with the wireless access point 103, and the mobile data offload from 3G to WiFi is enabled.
In the above process, the probe request 111 and the probe response 113 are invoked depending on the scenario. Normally, probe request is used when the mobile device proactively tries to search for APs to associate with.
In practice, allowable transmission power levels of WiFi usually vary from region to region. For example, according to FCC rules, 4W EIRP for isotropic PMP mode is allowed for US. EIRP levels of 20 dBm are allowed in the EU. Based on these power levels, the range of a WiFi access point operating in the point to multipoint mode can reach a distance of about 1 km. This would make it feasible for mobile network operators to install their own specialized WiFi APs. Long range WiFi nodes can be installed sparsely in the exterior of buildings. With the long range WiFi, the service provider need not depend on the public WiFi APs, which is a nightmare when it comes to controlling quality of service, billing, installation and access management. Long range WiFi would therefore reduce cost and provide larger coverage foot print.
However, power levels in typical mobile client device, such as smartphones, are usually very low, which usually allow radio ranges of up to about 50 m in the uplink. In that case, for example, the requests 111, 115, 119 from the mobile client 101 in FIG. 1 may not be able to reach the AP 103 when the distance between the mobile client 101 and the AP 103 exceeds the uplink radio range, and therefore the 3G-WiFi offload may fail. The disparity in the radio ranges for the uplink and downlink transmission to the mobile client remains a problem.